In general, writing instruments having a structure in which they are provided with a ballpoint tip or a finely movable valve system in order to prevent a direct flow of an ink are employed in many cases for writing instruments having such a form that they comprise a writing instrument main body such as an ink vessel which is excellent in a display property and liable to observe an ink remaining amount, an ink and a follower (following member) filled at a rear end part of the ink.
In writing instruments in which the ballpoint pen tip is used to prevent a direct flow of an ink as is the case with the former structure, the ink is designed in many cases so that the ink is prevented from flowing directly from the tip when the tip is continuously brought into contact with a non-writing surface with the tip turned downward in storing, and it narrows a width of designing the ink.
Also, in the writing instrument of the valve system employed in the latter structure, a writing feeling is deteriorated due to backlash caused in writing, and a flow amount of an ink is varied depending on time for which the valve is opened. Accordingly, the problem that a difference in a density of lines in writing characters and straight lines is liable to be brought about has been involved therein.
Known as writing instruments which intend to try to solve such the problem as described above are, for example,
1) a writing instrument of a valve system provided with a valve mechanism in which the valve is opened to cause an ink in an ink reservoir to flow to a pen feed in a case where a pen feed moves back at a fixed stroke or more and where a pressing force of a specific resistance load or more is applied in order to provide a writing instrument which makes it possible to smoothly open the valve without causing an uncomfortable feeling such as a pumping feeling and which has a sufficiently high spring force for closing the valve to make it possible to surely prevent the ink from leaking and dripping, wherein it is provided with a mechanism in which a dummy pumping part comprising an elastic member increasing a resistance load against a pressing force of the pen feed according to backward moving operation of the pen feed during a stroke applied until the valve is opened is provided at a tip part of a holder (refer to, for example, a patent document 1),2) a liquid storing vessel in a liquid discharge instrument, which receives a liquid in an inside and is connected with a discharge means for discharging the above liquid and which is provided with an air flow means for introducing thereinto air corresponding to a volume of the content liquid consumed as the content liquid is consumed through the discharge means, wherein an air exchange wall comprising organopolysiloxane which is a solid at ordinary temperature is arranged as the air flow means described above, and a minimum distance required for connecting an inside and an outside of the vessel described above is 1.0 μm or more and 0.2 mm or less (refer to, for example, a patent document 2),3) a writing instrument comprising an air flow passage which connects with an inside of an ink tank receiving an ink in a free state and which is formed for introducing air from the outside in order to maintain an internal pressure of the ink tank according to a change in a volume of the ink in the ink tank as the ink is consumed, wherein a viscous fluid layer comprising a viscous fluid in which a contact angle θ of the fluid formed with a wall member brought into contact with the fluid is 0<θ≦90° and in which a surface tension α is 10 dyn/cm≦α≦73 dyn/cm (20° C.) is arranged in the air flow passage described above, and an air flow hole is formed temporarily in the viscous fluid layer as an internal pressure of the ink tank is reduced according to a change in a volume of the ink (refer to, for example, a patent document 3),4) a writing instrument comprising an inner tube which receives directly an ink in a fluid manner and in which a rear end is opened, an outer tube in which the above inner tube is disposed in a coaxially and freely fitting manner so that a space of a prescribed cross-sectional area communicating with the outside via an air exchange means is secured between the inner tube and the outer tube and in which a rear end is closed, and a pen tip disposed at a front end aperture of the outer tube and the inner tube, wherein a balance liquid for controlling a flow pressure of the ink applied to the pen tip to a fixed pressure is received in a fluid manner at a latter part side of the space described above in an inside of the outer tube connecting via a rear end aperture of the space in an inside of the inner tube in a state connecting from an interface of the ink in the space of the inner tube (refer to, for example, a patent document 4), and5) a writing instrument in which an ink received in an ink reservoir in a fresh ink state is supplied to a pen tip and in which a movable wall part is provided at a wall part forming the ink reservoir so that the ink reservoir is decreased in a volume as the ink is consumed, wherein the movable wall part described above is provided at a wall part partitioning the ink reservoir, and an air chamber having an elastic wall part and a wall part forming a liquid film by a capillary force at a wall part partitioning the outside is provided (refer to, for example, a patent document 5).
The respective writing instruments described in the above patent documents 1 to 5 are improved more than writing instruments having conventional structures and enhanced in performances thereof, but an ink direct flow phenomenon is still observed, and therefore they are not satisfactory.
Also, in the patent document 5 described above in which the technology close to that of the present invention is disclosed, an elastic film member for meeting a change in an internal pressure is provided. However, when the above elastic film member is not provided with a repellent force (restoring force), an increased portion of a pressure applied by permeation can not be suppressed. Also, when an outside pressure is lower than an atmospheric pressure, an internal pressure falls into a pressurization state, and even if the outside pressure is lowered within the atmospheric pressure, the internal pressure falls into a pressurization state when heated subsequently. Further, if the elastic film member is provided with a repellent force, the internal pressure falls into a pressurization state due to the repellent force when a volume thereof is increased by a change in the temperature, and since the above elastic film member does not yet sufficiently meet a change in an internal pressure, problems such as causing leakage of an ink in use in a certain case are involved therein.